While the Android Device Manager could currently be used for locating the smartphones, the service has now got an additional feature which can be used to lock the device remotely.
The new feature on the Android Device Manager, which can be used to locate the Android device, allows to remotely lock the device with a unique password (not your account password), which would automatically override the existing screen unlock methods. However the feature requires explicit permission in the Google Settings app to lock the device remotely.
On locking the device using the web interface of the Android Device Manager, the phone would automatically get locked and would require the newly set password to be unlocked again. You can try the new feature using the Android Device Manager on the web. Similarly, CyanogenMod has unveiled similar features in their latest build.